Understanding Liver Function Tests
Learn what liver function tests measure, what the key markers mean, and how clinical scoring systems assess liver disease severity.
What Are Liver Function Tests?
Liver function tests (LFTs) are a group of blood tests that help evaluate the health and function of the liver. Despite the name, some of these tests measure liver damage rather than function. The standard panel typically includes alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), total bilirubin, albumin, and total protein. Together, these markers paint a picture of how well the liver is working and whether it has been injured.
Key Markers Explained
ALT and AST are enzymes released when liver cells are damaged — elevated levels suggest hepatocellular injury. ALT is more specific to the liver, while AST is also found in the heart and muscles. ALP and GGT rise in conditions affecting the bile ducts (cholestatic disease). Bilirubin is a waste product from red blood cell breakdown; elevated levels cause jaundice and indicate impaired liver processing. Albumin, a protein made by the liver, decreases in chronic liver disease and reflects the liver's synthetic capacity.
Common Patterns and What They Suggest
A hepatocellular pattern shows markedly elevated ALT and AST with relatively normal ALP — this is typical of viral hepatitis, drug toxicity, or ischemic liver injury. A cholestatic pattern shows elevated ALP and GGT with milder transaminase elevation, suggesting bile duct obstruction or infiltrative disease. A mixed pattern involves elevations in both categories. The ratio of AST to ALT can also provide clues: a ratio greater than 2:1 is suggestive of alcoholic liver disease.
Liver Disease Severity Scoring
When chronic liver disease is present, clinical scoring systems help assess its severity and guide treatment decisions. The Child-Pugh score uses five variables — bilirubin, albumin, INR (a measure of blood clotting), ascites, and hepatic encephalopathy — to classify cirrhosis into three classes (A, B, C) of increasing severity. The MELD score (Model for End-Stage Liver Disease) uses bilirubin, creatinine, and INR to predict short-term mortality and prioritize patients for liver transplantation.
When to Be Concerned
Mildly elevated liver enzymes are common and may be caused by medications, fatty liver disease, or vigorous exercise. However, you should seek medical attention if enzyme levels are more than three times the upper limit of normal, if bilirubin is elevated (especially with jaundice), if albumin is low, or if abnormalities persist over multiple tests. Symptoms such as right upper abdominal pain, unexplained weight loss, dark urine, or pale stools also warrant prompt evaluation by a healthcare provider.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
Related Tools
Child-Pugh Score
Calculate the Child-Pugh score to classify the severity of chronic liver disease and estimate prognosis. Uses bilirubin, albumin, INR, ascites, and encephalopathy.
MELD Score
Calculate the MELD and MELD-Na scores to assess liver disease severity and transplant priority. Uses bilirubin, INR, creatinine, and sodium.